So I’ve tried to reproduce the test manually using the same command in the setup:Get-OwaMailboxPolicy -DomainController $RoleDomainController | where {$_.Identity -eq "Default"}
And the result was indeed $null .. which made no sense here… because it does exists, as the error states – the object ‘CN=Default,CN=OWA Mailbox Policies,CN=Exchange,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=domain,DC=com’ already exists.

Then I’ve noticed that the CN was “default” with lower “d” … although the Where-Object and -eq should be case insensitive, the check failed…